Staff directory Aitor Lopeandia Fernández

Aitor Lopeandia Fernández

UAB Senior Researcher
Thermal Properties of Nanoscale Materials



  • Dynamic electric-field-induced magnetic effects in cobalt oxide thin films: Towards magneto-ionic synapses

    Martins S., De Rojas J., Tan Z., Cialone M., Lopeandia A., Herrero-Martin J., Costa-Kramer J.L., Menendez E., Sort J. Nanoscale; 14 (3): 842 - 852. 2022. 10.1039/d1nr06210g. IF: 7.790

    Voltage control of magnetism via electric-field-driven ion migration (magneto-ionics) has generated intense interest due to its potential to greatly reduce heat dissipation in a wide range of information technology devices, such as magnetic memories, spintronic systems or artificial neural networks. Among other effects, oxygen ion migration in transition-metal-oxide thin films can lead to the generation or full suppression of controlled amounts of ferromagnetism ('ON-OFF' magnetic transitions) in a non-volatile and fully reversible manner. However, oxygen magneto-ionic rates at room temperature are generally considered too slow for industrial applications. Here, we demonstrate that sub-second ON-OFF transitions in electrolyte-gated paramagnetic cobalt oxide films can be achieved by drastically reducing the film thickness from >200 nm down to 5 nm. Remarkably, cumulative magneto-ionic effects can be generated by applying voltage pulses at frequencies as high as 100 Hz. Neuromorphic-like dynamic effects occur at these frequencies, including potentiation (cumulative magnetization increase), depression (i.e., partial recovery of magnetization with time), threshold activation, and spike time-dependent magnetic plasticity (learning and forgetting capabilities), mimicking many of the biological synapse functions. The systems under investigation show features that could be useful for the design of artificial neural networks whose magnetic properties would be governed with voltage. This journal is © The Royal Society of Chemistry.


  • Critical Role of Electrical Resistivity in Magnetoionics

    De Rojas J., Salguero J., Quintana A., Lopeandia A., Liedke M.O., Butterling M., Attallah A.G., Hirschman E., Wagner A., Abad L., Costa-Krämer J.L., Sort J., Menéndez E. Physical Review Applied; 16 (3, 034042) 2021. 10.1103/PhysRevApplied.16.034042. IF: 4.985

    The utility of electrical resistivity as an indicator of magnetoionic performance in stoichiometrically and structurally similar thin-film systems is demonstrated. A series of highly nanocrystalline cobalt nitride (Co-N) thin films (85 nm thick) with a broad range of electrical properties exhibit markedly different magnetoionic behaviors. Semiconducting, near stoichiometric CoN films show the best performance, better than their metallic and insulating counterparts. Resistivity reflects the interplay between atomic bonding, carrier localization, and structural defects, and in turn determines the strength and distribution of applied electric fields inside the actuated films. This fact, generally overlooked, reveals that resistivity can be used to quickly evaluate the potential of a system to exhibit optimal magnetoionic effects, while also opening interesting challenges. © 2021 American Physical Society.

  • Magneto-Ionics in Single-Layer Transition Metal Nitrides

    De Rojas J., Salguero J., Ibrahim F., Chshiev M., Quintana A., Lopeandia A., Liedke M.O., Butterling M., Hirschmann E., Wagner A., Abad L., Costa-Krämer J.L., Menéndez E., Sort J. ACS Applied Materials and Interfaces; 13 (26): 30826 - 30834. 2021. 10.1021/acsami.1c06138. IF: 9.229

    Magneto-ionics allows for tunable control of magnetism by voltage-driven transport of ions, traditionally oxygen or lithium and, more recently, hydrogen, fluorine, or nitrogen. Here, magneto-ionic effects in single-layer iron nitride films are demonstrated, and their performance is evaluated at room temperature and compared with previously studied cobalt nitrides. Iron nitrides require increased activation energy and, under high bias, exhibit more modest rates of magneto-ionic motion than cobalt nitrides. Ab initio calculations reveal that, based on the atomic bonding strength, the critical field required to induce nitrogen-ion motion is higher in iron nitrides (≈6.6 V nm-1) than in cobalt nitrides (≈5.3 V nm-1). Nonetheless, under large bias (i.e., well above the magneto-ionic onset and, thus, when magneto-ionics is fully activated), iron nitride films exhibit enhanced coercivity and larger generated saturation magnetization, surpassing many of the features of cobalt nitrides. The microstructural effects responsible for these enhanced magneto-ionic effects are discussed. These results open up the potential integration of magneto-ionics in existing nitride semiconductor materials in view of advanced memory system architectures. © 2021 American Chemical Society. All rights reserved.


  • Voltage-driven motion of nitrogen ions: a new paradigm for magneto-ionics

    de Rojas J., Quintana A., Lopeandía A., Salguero J., Muñiz B., Ibrahim F., Chshiev M., Nicolenco A., Liedke M.O., Butterling M., Wagner A., Sireus V., Abad L., Jensen C.J., Liu K., Nogués J., Costa-Krämer J.L., Menéndez E., Sort J. Nature Communications; 11 (1, 5871) 2020. 10.1038/s41467-020-19758-x. IF: 12.121

    Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics in Co3O4. Both materials are nanocrystalline (face-centered cubic structure) and show reversible voltage-driven ON-OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels. Remarkably, nitrogen magneto-ionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results may open new avenues in applications such as brain-inspired computing or iontronics in general. © 2020, The Author(s).